Process for preparing aminophenols



QPatented Aug. 10,1048

Frederic R. Bean, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y" a corporation of New Jersey No Drawing. Application July 29. 1944, Serial No. 547,296

This invention relates to a process for preparing aminophenols and more particularly to a process for preparing aminophenols from aromatic nitro compounds.

16 Claims. (Cl. 260-575) acids, especially those having a dissociation constant in water at 25 0. not smaller than that of oxalic acid (first hydrogen) can also be used.

, The acid employed should be one which does It is well known that nitrobenzene can be re- 5 not react, under the conditions of the process, duced to yield aniline by means of reducing with any hydroxylamine derivatives, since comagents comprising metals, such as iron, zinc and pounds of this type appear to be formed during tin, and aqueous solutions of mineral acids, such the process. For this reason, formic acid should as hydrochloric acid andsulfurlc acid. It is be avoided. The reduction of the aromatic nialso known that nitrobenzene can be reduced to tm compound with the aluminium and aqueyield phenylhydroxylamine by means of reducous solution of the mineral acid is-advanta ing agents comprising metals, such as aluminium, geously effected at a temperature oil from 50 to lead, zinc, and magnesium, and substantially 100 (3.. although the temperature is apparently neutral aqueous solutions of salts, such as amnot critical. Especially good results have been monium chloride, sodium chloride and calcium obtained at temperatures between about 80 C. chloride. Moreover, the phenylhydroxylamine and 100 C. In the case of high melting arothus produced can rt d t p-aminomatic nitro compounds, a water miscible solphenol by; heating: with aqueous mineral acids, ven h as ethyl alcohol, or a water immisthe latter step involving-the well known re'ar- Oible S v nt. such as a hydrocarbon, m y be n ement.of phenylhydroxylamme t p-amlnoadded to the reaction mlxtureto promote disphenol. Y persion in the aqueous acid.

It is also known .that nitrobenzene can be ree f ll w n ex mples will serve to illusduced to yield phenylhydroxylamine by dissolvirate the m nn r 0 pr t ng my. invention. m nitrobenzene in hot concentrated sulfuric These e amp es a e not ntended to mit y inacid and treating the hot. solution with zinc dust. Ventioh- 0n the other hand, as stated above, treatment 0! Ex mple .m-Aminophenol nitrobenzene with zinc and an aqueous solution .of sulfuric acid produces aniline. I have now found that treatment of nitrobenzene with aluminium and an aqueous solution 80 of a mineral acid gives principally-not aniline nor phenylhydroxylamine but rather p-aminophenol. In iother words, aluminium and an 3 aqueous solut on of a mineral acid acts quite differently from metals, such as zinc, iron and tin, 6? sag. fi ggigg fig gg gg gg in conjunction with an aqueous solution of a en e mneml acid I have also found that sulfuric acid (sp. g. 1.84). The resulting mixother ture was heated to 80 C to 100 C and vi or matic nitro compounds can be similarly conously stirred while 18 19 I .5 verted to aminophenolic compounds. flakes were slowl added g Zi It is, accordingly, an object of my invention 40 y g course 0 t two hours. No nitrobenzene remained after- 0 provide new process for preparing ammo three to four hours heatin and stirrin Th henols. Other objects will become apparent g geremafter reaction mixture was filtered to remove the small In accordance with the invention, an aromatic 22 83 gfl'l ggg igg g mg 53:51 2; nitro compound is treated with aluminium and of water. The total value of the filtrate and n aqueous so tio o an acid- The aluminium washings was between 1500 and 2000 'cc. The Y is advantagemlsly m a divided Such as hot filtrate and washing was made alkaline to flakes or a'powder. The aqueo s sol ti n of th brilliant yellow with sodium hydroxide or somineral acid contains not more than per cent dium carbonate and a few grams of sodium suly weight of aciden dv nta e u ly contains 50 fite, whereupon aluminium hydroxide precipitatnot more than about 15 per cent by weight of the ed. The mixture was heated to boiling and filacidi Sglfurc hacid is especially advantageously t r d hil t, p ye t er mineral acids can be em- The precipitate of aluminium h droxide wa P e e- 8- Ph ph ri acid- Hy roc ric d, washed with several 100 cc. portions of hot water generally speaking, is less satisfactory. Organic The combined filtrate and washing was evapo- 3 rated to about 800 cc., whereupon a small amount of e by-product separated out. The aniline was removed by steam distillation and the remaining solution was cooled to about 20 C., whereupon p-aminophenol separated outas white flakes. These flakes were filtered off, washed with water and dried in the air. The yield was 41 g. (75 per cent), exclusive of what remained in the mother-liquors. The p-aminophenol was found to contain 65.91 per cent of carbon, 6.3 per cent of hydrogen and 12.89 per cent of nitrogen (calculated for carbon 66.0 per cent, for' hydrogen 6.4 per cent and for nitrogen 12.8 per cent). The p-aminophenol melted at 184 C. with decomposition.

Instead of adding the aluminium flakes to a mixture of nitrobenzene, water and sulfuric acid,

a sulfuric acid solution in water can be added to a hot stirred suspension of aluminium and aqueous sulturic acid.

Example 2.5-Amino-2-hydrozybenzenesulfonic acid OrK

' arated out. This was filtered ofl and dried. The

yield was 15.5 g. When this product was dissolved inaqueous sodium hydroxide in the presence of a small amount of sodium sulfite and reprecipitated by adding hydrochloric acid to the solution, 14 g. of purified produce was obtained. This purified product was found to contain 38.01 per cent by weight of carbon (calculated38%); 3.86 per cent by weight of nitrogen (calculated 3.7%) and 7.34 per cent by weight of hydrogen (calculated 7.4%). This compound also acted as a photographic developer.

'Emmple 3.1,4-.4minonaphthol 21.5 g. of. c-nitronaphthalene were added to 500 cc. of water to which had been added 37.5 cc.

product remained after the ether extraction. Upon evaporating the ether from the ether extract, 3 g. of crystals were obtained. A portion of these crystals were recrystallized from chlorobenzene and melted at 190 to 191 C. These crystals were crystals of 1,4-dihydroxynaphthalene as further shown by analysis: carbon found 74.91 per cent (calculated 75%); hydrogen found 5.09 per cent (calculated 5%). The 17.5 g. of

ether-insoluble product was mixed with to cc. of water and 4 to 5 g. of sodium hydroxide and a small amount of sodium hydrosulfite. The alkali-insoluble portion was filtered off and shown to be a-naphthylamine. Yield 4.1 g. To the alkali-soluble portion was added sodium bisulfite and sodium hydrosulfite whereupon a precipitate 4 separated out. This product weighing 13.4 g. was

1,4-aminonaphthol. A portion was converted to the hydrochloride by mixing with concentrated hydrochloric acid. The hydrochloride was found to contain 60.99 per cent of carbon (calculated 61.37%), 6.92 per cent of nitrogen (calculated 7.16%) and 5.69 percent of hydrogen (calculated 5.75%). The product behaved as a powerful photographic developer.

Example 4.4-amino-3-methyl-1maphthol 9.3 g. .of 2-methyl-1-nitronaphthalene were added to 200 cc. of water to which had been added 15 cc. of concentrated sulfuric acid. The resulting mixture was held at about 90 C. while 2 g. of aluminium flakes were added slowly with vigorous stirring over a period cl. 1%; to 2 hours. Following the addition of aluminium, the reaction mixture was stirred and heated at 90 C. for 2 to 3 hours. The reaction mixture was then concentrated to a volume of 200 cc. The concentrated mixture was cooled to 5 C. and maintained at this temperature for about 48 hours.

The product which precipitated was filtered off and dried. 5.7 g. of product was thus obtained. This product was triturated with several 50 cc. portions of diethyl ether leaving 5.1 g. of ether in the soluble material (amine sulfates). The filtrate from the 5.7 g. of product was extracted with four 100 cc. portions of diethyl ether. Upon evaporating these combined ether extracts to dryness, 1.5 g. of product was obtained. Concentrated hydrochloric acid was added to this product and the mixture was again evaporated to dryness. The resulting residue was triturated with ether leaving 1 g. of an amine hydrochloride. The combined ether extracts from the above two triturations were evaporated to dryness and the residue was dissolved in dilute aqueous sodium hydroxide containing a small amount of sodium sulfite and a small amount of sodium hydrosulfite. The alkaline solution was decolorized with activated charcoal and filtered. To the filtrate was added sodium bisulfite in excess and the product which precipitated was filtered off. This ethersoluble product which weighed 0.5 g. was recrystallized from chlorobenzene. The recrystallized product melted at 174 to 175 C. Upon analysis, the product was found to contain 76.07 per cent by weight of carbon, and 6.03 per cent by weight of hydrogen. This analysis and melting point established that the compound was 1,4-dihydation of a small amount of the product in acetic acid with potassium dichromate and sulfuric acid. and pouring the reaction mixture into water, yellow needles separated. These needles melted at -104" C. and were found to contain the carbon and hydrogen required of 2-methyl naphthoquinone is. known anti-hemorrhagic) further establishing the identity of 1,4-dihydroxy-2-methylnaphthalene.

The two ether-insoluble products consisting of 5.1 g. of aminesulfates and 1 g. of amine hydrochlorides were added to a dilute solution of aqueous sodium hydroxide containing a small amount of sodium sulfite and a small amount of sodium hydrosulfite. The undissolvedproduct was. filtered ofi and carefully dried. It weighed 2 g. A portion of the insoluble product was converted to the hydrochloride and upon analysis oi the hydrochloride, the following values were found: carbon 67.93 per cent, hydrogen 6.15 per cent and nitrogen 7.39 per cent. This analysis established the product to be 1-amino-2-methylnaphthalene hydrochloride (calculated values: carbon 68.2%, hydrogen 6.25% and nitrogen 7.23%). The sodium hydroxide solution, which was obtained above, was decolorized with-- activated charcoal and then treated with sodium bisulfite in excess whereupon a precipitate separated out. The precipitate was filtered off and dried. 2 g. of prod- I uct were thus obtained. The product was converted to the hydrochloride and the hydrochloride was found to contain 62.51 per cent of carbon, 5.64 per cent of hydrogen and 6.48 per cent of nitrogen. This analysis established the product to be 4-amino-3-methyl-1-naphthol hydrochloride (calculated values: carbon 62.99%, hydrogen 5.77% and nitrogen 6.68%). This compound also acted as a photographic developer. This compound can also be oxidized readily to- 2-methyl naphthoquinone.

Example 5.2-ammo-5-hydrorydiphenyl 25 g. of o-nitrodiphenyl were added to 500 cc. of water to which had been'added 37.5 cc. of concentrated sulfuric acid. The resulting mixture was heated to about 90 C. and held at about this temperature while'5 g. of aluminium were added with vigorous stirring. After all of the aluminium had been added, heating at about 90 C. and stirring were continued for about one hour. Oily by-products separated and these were filtered oiT. The resulting solution was made alkaline with sodium carbonate and sodium sulfite. The precipitated aluminium hydroxide was then filtered ofl. Upon cooling, a crystalline product precipitated from the resulting solution. It melted at 115 to 118 C. It was found to contain 77.87 per cent of carbon, 5.77 per cent of hydrogen and 7.53 per cent of nitrogen. This analysis established the product to be 2-amino-5- hydroxydiphenyl (calculated values: carbon 77.8%, hydrogen 5.9% and nitrogen 7.56%).

This compound also acted as a photographic developer.

In a similar manner, the following aromatic aminohydroxy compounds have been prepared:

Starting Materials Aminohydroxy Compounds m-nitrotoiuene o-nitrotolucne m-uitroauisolo o-nitroanisole m-chloronitrobcnzcne o-chloroniirobenzcne o-nitroaoctophenonc m-n'itroaniiine m-nitrophenoi o-nitrodighenylether o-nitroet ylbenzene What I claim as my invention and desir to be secured by Letters Patent of the United States is:

1. A process for preparing an aminophenol comprising reducing a nitroaromatic compound containing no substituent in the para position to the nitro group by reacting .the nltroaromatic compound simultaneously with aluminium and an aqueous solution of an acid selected from the group consisting of sulfuric .acid, phosphoric acid and hydrochloric acid, said solution containing not more than 50 per cent by weight of said acid, the quantity of acid present being suflicient to maintain an acid reaction medium,'until after the reduction is finished.

2. A process for. preparing an aminophenol comprising reducing a nitroaromatic compound containing no substituent in the para position to the nitro group by reacting the nitroaromatic compound simultaneously with aluminium and anaqueous solution of an acid selected from the group consisting of sulfuric acid, phosphoric acid and hydrochloric acid. said solution containing not more than 10 per cent by weight of said acid, the quantity of acid present being sufficient; to maintain an acid reaction medium, until after the reduction is finished.

3. A process for preparing an aminophenoi comprising reducing a nitroaromatic compound containing no substituent in the para position to the nitro group by reacting the nitroaromatic compound simultaneously with aluminium and an aqueous solution of an acid selected-from the group consisting of sulfuric acid, phosphori-cacid and hydrochloric acid, at a temperature of from about 50 C. to about 100C" said solution containing not more than about 50 per cent by weight of said acid, the quantity of acid being sufiicient to maintain an acid reaction medium until after the reduction is finished.

4. A process for preparing an aminophenol comprising reducing a nitroaromatic compound containing no substituent in the para position to the nitro group by reacting the nitroaromatic compound simultaneously with aluminium and an aqueous solution of an acid selected from the group consisting of sulfuric acid, phosphoric acid and hydrochloric acid, at a temperatur of from about C. to about C., said solution containing not more than about 50' per cent by weight of said acid, the quantity of acid being suiiicient to maintain an acid reaction medium prising .reducing nitrobenzene by reacting thenitrobenzene simultaneously with aluminium and I an aqueous solution of sulfuric acid containinB not more than per centbymveight oi the sulfuric acid, the quantity of acid present being suificientj to maintain an acid reaction medium until after the reduction is finished. v

I. A process for preparing p-aminophenol comprising reducing nitrobenzene by reacting, at a temperature or from about 50 C. to about 100 C.,

the nitrobenzene simultaneously with aluminium and an aqueous solution of sulfuric acid containing not more than 10 per cent by weight of the a sulfuric acid. the quantity of acid present being 'sufiicient to maintain-"an acid reaction medium until after the reduction is finished. 1

- 8. A process for preparing p-aminophenol comprising-reducing nitrobenzene by'reacting; at 'a temperature or about 80 C. to about 100 0., the i nitrobenzene Simultaneously with aluminium and an aqueous solution of sulfuric acid containing not more than 10 per cent by weight of the suliuric acid, the quantity of acid present being sufficie'nt to maintain an acid reaction medium until after the reductionisfinished;

9. A process for preparing 1, 7 comprising reducing a-nitronaphthalene by reacting the u-nitronaphthalene simultaneously with aluminium and an aqueous solution 9f suliuric acid containing not more than 50 per cent by weight of sulfuric acid;

10. A process for preparing 1,4-aminonaphthol I comprising reducing a-nitronaphthalene by reacting the a-nitronaphthalene simultaneously with aluminium and an aqueous solution of suliurio acid containing not morethan 10 per cent by weight or sulfuric acid, the quantity of acid present being sufficient to maintain an acid reac- -tion medium until after the reduction i finished. 11. A process for preparing 1,4-aminonaphthol comprising reducing a-nitronaphthalene by reacting, at a temperatureor about 50 C. to about 100 C., the a-nltronaphthalene simultaneously with aluminium and an aqueous solution of suli'uric acid containing not more than 10 per cent by weight 01' sulfuric acid, the quantity of acid present being suflicient to maintain an acid reaction medium until after the reduction is fin ished.

12. A process for preparing 1,4-aminonaphthol v comprising reducing a-nitronaphthalene by reacting. at a temperature of about 80 C. to about 100 0., the a-nitronaphthalene simultaneously with aluminium and an aqueous solution of 5111-.

furic acid containing not more than 10 per cent by weight of the sulfuric acid, the quantity of acid present being sufficient to maintain an acid re-v aminonaphiihol i a ammo action medium uaui after the uncertain finished.

18. A process for preparing d-amino-S-methyll-naphthol comprising reducing. 2-methyl-1- 5 nitronaphthaicne by reacting the z-methyl-lnitronaphthaiene simultaneously with aluminium and an aqueous solution of sulfuric acid containing not more than per cent by weight or the sulfuric acid, the quantity or. acid present being sufiicient to maintain an acid reaction medium until after the reduction is finished.

14. A process-for preparing e-aminca-methyl- 1- naphthoi comprising reducing z-methyl-lnitronaphthalene by reacting the 2-methyl-1- nitronaphthalene simultaneously with aluminium and an aqueous solution of sulfuric acid containing not more than 10 per cent by weight of the sulfuric acid, the quantity oi acid present being sufiicient ,to maintain an acidreacticn medium until after the reduction is finished.

l-naphthol comprising reducing 2-methyl-1- nitronaphthalene by reacting the 2-methyl-1- nitronaphthaiene, at a temperature oi. about C. to about 100.C., simultaneously with aluminium and an aqueous solution of sulfuric acid containing not more than 10 per cent by weight of the sulfuric acid, the quantity of acid present being suflicient to maintain an acid reaction medium until after the reduction is finished.

16. A process for preparing 4-amino-3-methyll-naphthol comprising reducing 3-methyl-lnitronaphthalene by reacting the 2-methyl-1- nitronaphthalene, at a temperature 0! about C. to about C.,simultaneously with aluminium andan aqueous solution of sulfuric acid containing not more than 10 per cent by weight of the sulfuric acid, the quantity of acid present being sufiicient to maintain an acid reaction medium until after the reduction is finished.

. FREDERIC R. BEAN.

unrnnnncns orrnn The following references are of record in the file of this patent: a

STATES PATENTS Number Germany Mar. 15, 1898 15. A pro'cessfor preparing 4-amino-3-methyl- 

